This invention relates to a method of producing ultra-hard abrasive particles, particularly diamond particles.
Methods of producing diamond and cubic boron nitride abrasive particles synthetically are well known in the art. The methods can be tailored to produce particles having particular characteristics. For example, the method may be tailored to produce friable diamond particles which are used in applications such as grinding. Alternatively, the method may be tailored to produce a strong blocky diamond of good quality. Such diamonds are typically used in saws and grinding applications.
Diamonds are synthesised by subjecting a carbon source i.e. a precursor of diamond, to elevated temperature and pressure conditions at which diamond is crystallographically stable, generally in the presence of a diamond solvent catalyst. Similarly, cubic boron nitride particles are synthesised by subjecting hexagonal boron nitride, i.e. the precursor of cubic boron nitride, to elevated temperature and pressure conditions at which cubic boron nitride is crystallographically stable in the presence of a solvent/catalyst for cubic boron nitride.
describes a method of synthesising diamond particles by coating fine diamond particles with at least one layer of a non-diamond carbon material, a catalyst/solvent in the form of a metal powder and an organic binder, compacting the coated particles in such a manner that they are at least partially in contact with each other, placing the compacted arrangement in a suitable synthesising vessel and subjecting the compacted arrangement to temperature and pressure conditions at which diamond is crystallographically stable.
The diamond which is synthesised is a relatively large diamond. This method of producing relatively large diamonds has several drawbacks. First, the fine particles are difficult to coat, particularly using the fluidisation method described in the patent. As a consequence, agglomeration of the seeds tends to occur. If larger particles are used as the seed, remnants of the seed can appear visibly in the synthesised diamond. Further, the seeds in the compacted arrangement are exposed to a variable environment during the growth stage. This variability results in variability in the diamond synthesised.